Distribution of activity in spinal pathways evoked by experimental dorsal column stimulation

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✓ Experiments were performed in rhesus monkeys to determine the distribution of activity evoked in spinal pathways by dorsal column stimulation. It was shown that many pathways in both the dorsal and ventral quadrants of the cord can be activated either directly or transsynaptically by stimulation with electrodes of the type implanted clinically. Moreover, the transsynaptically evoked responses recorded in each quadrant had somewhat different characteristics. Therefore, since the activation of each group of pathways may have differing effects in modifying the perception of noxious stimuli, the authors believe that changes in electrode position and stimulus parameters may be important in obtaining the therapeutic value of spinal cord stimulation for relief of pain.

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Address reprint requests to: James R. Bloedel, M.D., Ph.D., Department of Neurosurgery, B-590 Mayo Memorial Building, University of Minnesota, Minneapolis, Minnesota.

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    Recording of responses evoked in the dorsal columns by stimuli applied at different frequencies with a tinsel bipolar (left column) and 3-element bipolar (right column) electrode. Stimulus frequencies for both columns are shown on the far left. In this and all subsequent records the arrow marks the time at which the stimulus is applied and negative voltage is upward. Responses were summed 128 times. DC = dorsal column.

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    Recording of responses evoked in the dorsal columns by stimuli applied at different strengths with a tinsel bipolar (left column) and 3-element bipolar (right column) electrode. Stimulus voltages are indicated on the far left. Responses were summed 128 times. DC = dorsal column.

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    Recording of responses evoked in the dorsolateral fasciculus by stimuli applied at different frequencies with a tinsel bipolar electrode. Notice the decrease in amplitude of the small, long-latency negativity as the stimulus frequency is increased. DC = dorsal column.

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    Recordings of responses in the dorsal quadrant (DQ) and the ventral quadrant (VQ) made with a microelectrode following stimulation with a tinsel bipolar electrode. Frequency and voltage of the stimulus were 20 Hz and 4 V, respectively. The proposed transsynaptically evoked response is marked with a star. DC = dorsal column.

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    Recordings of responses in the ventral quadrant (VQ) following stimulation with a bipolar tinsel electrode at different strengths (left column) and frequencies (right column). In the study shown on the left, the time of occurrence of the initial peak negativity is marked by line a. The time at which the second peak negativity occurred at the lowest stimulus strength (4 V) is indicated with line b. Recording on the right shows the effects of increasing the stimulus frequency on the responses indicated by the closed and open circles. DC = dorsal column.

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